1. Field of the Invention
The present invention relates to a fluorescent X-ray analysis apparatus for carrying out element analysis and composition analysis of a measured sample by irradiating a primary X-ray on the measured sample, inducing the fluorescent X-ray from the measured sample, and measuring energy of this fluorescent X-ray and intensity of the X-ray.
2. Description of the Related Art
A conventional general fluorescent X-ray analysis apparatus will be described with reference to FIG. 10. Across a horizontal measured sample base 1003, a measured sample 1005 is arranged upward of the measured sample base 1003 and an X-ray source 1001, a primary filter 1002, and a detector 1007 are arranged downward of the measured sample base 1003. A reference numeral 1004 denotes a primary X-ray irradiated from the X-ray source 1001, and a reference numeral 1006 denotes a fluorescent X-ray generated when the measured sample 1005 is exited by the primary X-ray 1004. In this way, conventionally, the irradiated surface of the primary X-ray on the surface of the measured sample and the surface opposed to the detector on the surface of the measured sample are on the same plane.
In addition, it is general that a detection efficiency of the fluorescent X-ray from the focused element is improved by approaching the detector and the X-ray source to the measured sample as much as possible.
In addition, the apparatus having a primary filter in order to improve a ratio between a peak intensity of the fluorescent X-ray of the focused element and a background intensity mainly based on a scattered X-ray or the like (hereinafter, referred to as a peak-back ratio); the apparatus using a secondary target; and the apparatus using an optical device for making the X-ray into monochrome and focusing the X-rays are provided, however, all of them have the structure such that the detector is opposed to a point where the primary X-ray is irradiated (for example, refer to JP-A-2004-150990 (P.3 and FIG. 1)).
In the conventional fluorescent X-ray analysis, it is general to improve a peak-back ratio by using the primary filter when confirming a presence of a trace heavy metal such as cadmium contained in a light element major component which is composed of C, O, and H or the like and a density thereof. The present method is very useful, however, the primary X-ray is attenuated by inserting the primary filter and as a result, the intensity that the fluorescent X-ray of the trace heavy metal exited by the measured sample enters the detector is low.
Therefore, in order to make the intensity of the X-ray entering the detector stronger, the structure of approaching the detector and the X-ray source to the measured sample is applied. However, since both of the detector and the X-ray source are arranged so as to be opposed to the same plane on the surface of the measured sample, there is a limitation in a distance for approaching due to interruption of the both structural objects when approaching them to the measured sample. Therefore, it is general that a detection limit is several wt pap in measurement of several hundreds seconds when measuring a trace heavy metal in a light element.
In order to improve the detection limit of the trace heavy metal, a peak-back ratio is an important factor, however, volume of the intensity of the obtainable X-ray, namely, the sensitivity thereof is also an important factor. Hereinafter, a general formula of the detection limit is described. When the intensity of the X-ray is increased, in proportion to this, the background intensity and sensitivity are increased. In other words, from the following formula, the detection limit is improved (lowered) in inverse proportion to a root of the obtained intensity of the X-ray.
                              DL          =                                    3              ⁢              σ                        S                          ⁢                                  ⁢                              σ            =                                                            n                  BG                                                  T                  LT                                                              ,                                          ⁢                      S            =                                                            n                  P                                -                                  n                  BG                                                            C                i                                                                        [                  Formula          ⁢                                          ⁢          1                ]            
Here, DL denotes a Detection Limit, np denotes peak intensity, nBG denotes background intensity, TLT denotes Live Time, and Ci denotes density of a focused element.